29 research outputs found
Measurement of Angular Distributions and R= sigma_L/sigma_T in Diffractive Electroproduction of rho^0 Mesons
Production and decay angular distributions were extracted from measurements
of exclusive electroproduction of the rho^0(770) meson over a range in the
virtual photon negative four-momentum squared 0.5< Q^2 <4 GeV^2 and the
photon-nucleon invariant mass range 3.8< W <6.5 GeV. The experiment was
performed with the HERMES spectrometer, using a longitudinally polarized
positron beam and a ^3He gas target internal to the HERA e^{+-} storage ring.
The event sample combines rho^0 mesons produced incoherently off individual
nucleons and coherently off the nucleus as a whole. The distributions in one
production angle and two angles describing the rho^0 -> pi+ pi- decay yielded
measurements of eight elements of the spin-density matrix, including one that
had not been measured before. The results are consistent with the dominance of
helicity-conserving amplitudes and natural parity exchange. The improved
precision achieved at 47 GeV,
reveals evidence for an energy dependence in the ratio R of the longitudinal to
transverse cross sections at constant Q^2.Comment: 15 pages, 15 embedded figures, LaTeX for SVJour(epj) document class
Revision: Fig. 15 corrected, recent data added to Figs. 10,12,14,15; minor
changes to tex
Observation of a Coherence Length Effect in Exclusive Rho^0 Electroproduction
Exclusive incoherent electroproduction of the rho^0(770) meson from 1H, 2H,
3He, and 14N targets has been studied by the HERMES experiment at squared
four-momentum transfer Q**2>0.4 GeV**2 and positron energy loss nu from 9 to 20
GeV. The ratio of the 14N to 1H cross sections per nucleon, known as the
nuclear transparency, was found to decrease with increasing coherence length of
quark-antiquark fluctuations of the virtual photon. The data provide clear
evidence of the interaction of the quark- antiquark fluctuations with the
nuclear medium.Comment: RevTeX, 5 pages, 3 figure
Determination of the Deep Inelastic Contribution to the Generalised Gerasimov-Drell-Hearn Integral for the Proton and Neutron
The virtual photon absorption cross section differences [sigma_1/2-sigma_3/2]
for the proton and neutron have been determined from measurements of polarised
cross section asymmetries in deep inelastic scattering of 27.5 GeV
longitudinally polarised positrons from polarised 1H and 3He internal gas
targets. The data were collected in the region above the nucleon resonances in
the kinematic range nu < 23.5 GeV and 0.8 GeV**2 < Q**2 < 12 GeV**2. For the
proton the contribution to the generalised Gerasimov-Drell-Hearn integral was
found to be substantial and must be included for an accurate determination of
the full integral. Furthermore the data are consistent with a QCD
next-to-leading order fit based on previous deep inelastic scattering data.
Therefore higher twist effects do not appear significant.Comment: 6 pages, 3 figures, 1 table, revte
Engineering: Cornell Quarterly, Vol.13, No.3 (December 1978): Planets and their Satellites
IN THIS ISSUE: Exploring New Worlds in Space: The Other Moons /2
Joseph A. Burns, associate professor of theoretical and applied mechanics, and Joseph Veverka, associate professor of astronomy, discuss what has been learned about the natural satellites of the solar system and what may be anticipated from
the Voyager and Galileo missions.) ... Phobos: A Captured, Fractured Asteroid? /11 (A Cornell Ph.D. dissertation in geological sciences, a photointerpretive study of Viking Orbiter pictures of the moons of Mars, is the basis of this article. Peter Thomas, now a research associate at Cornell's Center for Radiophysics and Space Research, wrote the thesis; Arthur L. Bloom, professor of geological sciences, was chairman of his graduate committee.) ...
Clues to an Understanding of Volcanism /18 (Studies of volcanism on Earth may profit from comparative studies of volcanism on other planets and their satellites, as well as on Earth's Moon, according to Donald L. Turcotte, professor of geological sciences.) ... Cold Skin and a Warm Heart: A Model for Earth's Moon /26 (Arthur F. Kuckes, professor of applied and engineering physics, explains his study of magnetometer data obtained in the Apollo program, and his conclusions about
convection in the Moon.) ... Register /33 ... Vantage /41 (Engineering strength in soccer and football is recognized in a prejudiced look at this year's Cornell teams.) ... Faculty Publications /4